Methods and apparatus for controlling mask leak in cpap treatment

ABSTRACT

A method of operating a device for treating sleep disordered breathing (SDB), wherein the device provides continuous positive airway pressure during sleep, includes determining whether treatment pressure at the patient interface is below a desired value, in response to the determining, increasing pressure generated by the flow generator, in response to the increasing, making a determination that the increase in flow generator pressure has resulted in less than a desired increase in treatment pressure at the patient interface, and in response to the determination, reducing or inhibiting further increase of the flow generator pressure.

This application is a continuation of U.S. application Ser. No.11/921,753, filed Dec. 7, 2007, now allowed, which is the U.S. nationalphase of International Application No. PCT/AU2006/000823, filed Jun. 14,2006 which designated the U.S. and claims priority to AustralianApplication No. AU2006900774, filed Feb. 16, 2006, AustralianApplication No. AU2005903089, filed Jun. 14, 2005, AustralianApplication No. 2005906122, filed Nov. 4, 2005, and AustralianApplication No. 2005906193, filed Nov. 8, 2005, each of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to mechanical ventilation of sleep disorderedbreathing (5DB), and in particular to methods and apparatus forimproving patient compliance in Continuous Positive Airway Pressure(CPAP) treatment.

2. Description of Related Art

A comprehensive background discussion of mechanical ventilation can befound in “Principles and Practice of Mechanical Ventilation” (1994)edited by Martin J Tobin, published by McGraw-Hill Inc., ISBN0-07-064943-7.

The use of nasal Continuous Positive Airway Pressure (CPAP) to treatObstructive Sleep Apnea (OSA) was invented by Cohn Sullivan, see U.S.Pat. No. 4,944,310. Generally, the treatment involves providing a supplyof air or breathable gas from a blower to a patient via an air deliveryconduit and a patient interface, such as a full-face or nasal mask, ornasal prongs. While treatment is effective, some patients find ituncomfortable. Improving patient comfort and compliance is a continuingchallenge.

One way to improve comfort is to provide a more comfortable patientinterface. In this regard, the ResMed MIRAGE™ masks have providedsignificant improvement in comfort. See U.S. Pat. Nos. 6,112,746;6,357,441; 6,581,602; and 6,634,358. A more recent development is theResMed MIRAGE™ ACTIVA™ mask series. See International Patent ApplicationWO 2001/97893.

In the early days of nasal CPAP systems for treating OSA, patients werefirst titrated in a clinical study to determine an optimal treatmentpressure. Titration involves a patient sleeping overnight in a clinicand being tested with a mask and CPAP device. The treatment pressureprovided by the CPAP device is adjusted until apneas are eliminated. Thetreatment pressure is usually in the range of 4-20 cmH₂O. A device wouldbe set to that pressure and given to the patient to take home. Asubsequent development was the automatically adjusting device that apatient could take home. The automatically adjusting device will raiseand/or lower the treatment pressure based on indications of obstructivesleep apnea, such as snoring. Such CPAP devices are sometime genericallyreferred to as Automatic Positive Airway Pressure (APAP) devices. SeeU.S. Pat. Nos. 5,245,995; 6,398,739; and 6,635,021.

Another type of nasal CPAP device provides a first pressure duringinhalation (sometimes termed an IPAP) and a second, lower pressureduring exhalation (sometimes termed an EPAP). Examples of these includethe ResMed VPAP™ series, and the Respironics BiPAP series. Bilevel CPAPdevices may be prescribed for patients who do not comply with singlepressure CPAP devices. Some patients perceive that the lower pressureduring exhalation is more comfortable, at least while they are awake.

Another way of improving patient comfort and compliance is to start eachtherapy session at a low therapeutic pressure, e.g., 4 cmH₂O, and rampup to fill therapeutic pressure over the first hour, to allow thepatient to adjust to the sensation while falling asleep. Alternatively,the device may set to implement a time delay before fill therapeuticpressure is applied, to allow the patient time to fall asleep beforefull therapeutic pressure is applied. See U.S. Pat. Nos. 5,199,424 and5,522,382.

Another form of automatically adjusting CPAP device is the ResMedAUTOSET™ SPIRIT™ device. In this device, the CPAP pressure isautomatically increased or decreased in accordance with indications offlow limitation, such as flow flattening, snore, apnea and hypopnea. SeeU.S. Pat. Nos. 5,704,345; 6,029,665; 6,138,675; and 6,363,933. Anadvantage of an automatically adjusting system is that over time thetreatment pressure required may vary for a particular patient and acorrectly functioning automatic system can obviate the need for thepatient to return for a subsequent sleep study. These patents alsodescribe a method and apparatus for distinguishing between so-called“central” and obstructive apneas.

The contents of all of the aforesaid patents are incorporated bycross-reference.

Some OSA patients find treatment with the above devices uncomfortableand they become non-compliant with the therapy. Other patients such ascardiovascular patients with Congestive Heart Failure, patients with REMHypoventilation, and patients with Respiratory Insufficiency could alsobenefit from a more comfortable and/or effective form of therapy.

One hurdle to patient acceptance of the therapy is in the initialfitting of the patient interface (e.g., mask), where the mask fit istested under relatively low pressure and high flow. This may result innoisy operation of the device and high flow air leaks as the mask isadjusted to the patient, which can be a noisy and unsettling initialexperience for the patient.

Another impediment to patient comfort and compliance may be the patientor bed partner being disturbed by air leaks from the mask.

SUMMARY OF THE INVENTION

One aspect of the invention relates to a method and apparatus toovercome or ameliorate one or more of these disadvantages.

Mask Leak Control

A first aspect of the invention relates to a method of operating adevice for treating sleep disordered breathing (SDB), wherein saiddevice provides continuous positive airway pressure during sleep, themethod comprising:

-   -   determining whether treatment pressure at the patient interface        is below a desired value;    -   in response to said determining, increasing pressure generated        by the flow generator;    -   in response to said increasing, making a determination that the        increase in flow generator pressure has resulted in less than a        desired increase in treatment pressure at the patient interface;        and    -   in response to said determination, reducing or inhibiting        further increase of the flow generator pressure.

A further aspect of the invention relates to a method of operating adevice for treating sleep disordered breathing (SDB), wherein saiddevice provides continuous positive airway pressure during sleep, themethod comprising:

-   -   determining whether treatment pressure at the patient interface        is below a desired value;    -   in response to said determining, increasing pressure generated        by the flow generator;    -   in response to said increasing, making a determination that the        increase in flow generator pressure has resulted in a greater        than desired increase in air leak from the patient interface, or        has increased the air leak from the patient interface; and in        response to said determination, reducing or inhibiting further        increase of the flow generator pressure.

In one form, making a determination is made by comparison of a mask leakparameter to a mask leak threshold. The mask leak parameter may be amask leak impedance parameter.

In an embodiment, the mask leak threshold is determined with referenceto a patient arousal index, such as an Apnea Hypopnea Index (AHI),and/or a sleep phase index of the patient.

A further aspect of the invention relates to a method of operating adevice for treating sleep disordered breathing (SDB), wherein saiddevice provides continuous positive airway pressure during sleep, themethod comprising:

-   -   comparing a mask leak parameter to a mask leak threshold to        determine excessive leak at the patient interface;    -   in response to said determination of excessive leak, reducing        the flow generator pressure; and    -   continuing to compare said mask leak parameter to said mask leak        threshold at said reduced flow generator pressure.

In an embodiment, the mask leak parameter is a mask leak impedanceparameter.

In one embodiment, reducing the flow generator pressure includesreducing the pressure to a ramp start pressure, and the method furtherincludes ramping up the pressure to a treatment pressure over apredetermined ramp time while continuing to compare the mask leakparameter to the mask leak threshold.

The method may further include halting the pressure ramping upon furtherdetermination of excessive leak at the patient interface.

In another embodiment, reducing the pressure includes reducing thepressure by a pressure increment to a first reduced pressure, andoptionally incrementally further reducing the pressure if excessive leakis detected at the first reduced pressure.

A further aspect of the invention relates to a method of assessing thefit of a patient interface (e.g., a mask) to a patient for a device fortreating sleep disordered breathing (SDB), wherein said device providescontinuous positive airway pressure during sleep, the method comprising:

-   -   generating a treatment pressure at a flow generator of the        device;    -   limiting gas flow applied to the patient to a predetermined flow        rate;    -   determining that treatment pressure at the patient interface is        below a desired value; and    -   making a determination that the seal of the patient interface to        the patient is inadequate.

In an embodiment, the flow rate is determined with reference to a ventflow rate of the patient interface.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings facilitate an understanding of the variousembodiments of this invention. In such drawings:

FIG. 1 illustrates a ventilator apparatus according to an embodiment ofthe present invention for implementing methods according to embodimentsof the invention;

FIG. 2 is a graph of a mask pressure against blower set pressure,showing mask leak; and

FIG. 3 is a flowchart illustrating mask leak control according to anembodiment of the invention.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS Hardware

A positive airway pressure (PAP) device in accordance with an embodimentof the invention includes a blower and blower-controller. The blower candeliver a supply of air at positive pressure 2-40 cmH₂O, but generallyin the range of 4-20 cmH₂O to a patient interface via an air deliveryconduit.

The device also includes a flow sensor to measure the flow of air alongthe conduit, and pressure sensors to measure the pressure of air at theblower outlet.

In one form, the device alternatively includes an additional pressuresensor to detect the pressure in the patient interface.

For example, FIG. 1 illustrates a ventilator device according to anembodiment of the invention. As illustrated, the ventilator device mayinclude a servo-controlled blower 2, a flow sensor 4 f, pressure sensor4 p, a mask 6, and an air delivery conduit 8 for connection between theblower 2 and the mask 6. Exhaust gas is vented via exhaust 13.

Mask flow may be measured by a flow sensor, such as a pneumotachographand differential pressure transducer to derive a flow signal F(t).Alternatively, the pneumotachograph may be replaced by a bundle of smalltubes aligned in parallel with the flow from the blower with thepressure difference measured by the differential pressure transduceracross the bundle.

Mask pressure is preferably measured at a pressure tap using a pressuretransducer to derive a pressure signal P_(mask)(t). The pressure sensor4 p and flow sensor 4 f have been shown only symbolically in FIG. 1since it is understood that those skilled in the art would understandhow to measure flow and pressure.

Flow F(t) and pressure P_(mask)(t) signals are sent to a controller ormicroprocessor - referred to herein as processor 15—to derive a pressurerequest signal P_(Request)(t). The controller or processor is configuredand adapted to perform the methodology described in more detail herein.The controller or processor may include integrated chips, a memoryand/or other instruction or data storage medium to implement the controlmethodology. For example, programmed instructions with the controlmethodology are either coded on integrated chips in the memory of thedevice or loaded as software. As those skilled in the art willrecognize, analogue devices may also be implemented in the controlapparatus.

The controller or processor 15 is further adapted to derive parametersindicative of the patient's breathing and sleep pattern, such as forderiving indications of flow limitation, such as flow flattening, snore,apnea and hypopnea and the Apnea Hypopnea Index (AHI), and fordistinguishing between REM and non-REM sleep. See U.S. Pat. Nos.5,704,345 and 6,029,665.

The apparatus of FIG. 1 includes other sensors, communication interfacesand displays, a servo, etc., and functional blocks the details of whichare not necessary for an understanding of the present invention.

In an embodiment, the controller may be programmable by the clinicianusing the menu system to alter the parameters of the ‘first timer’ mode,for example, to set the initial therapy session pressure and/or thedaily pressure increment according to the severity of the patient'ssleep disordered breathing and the clinician's opinion of how long thepatient may take to acclimatize to the sensations of the CPAP therapy.

At the commencement of the therapy session, the session timer of thecontroller is started.

Where the flow generator is of the type which provides for this, andwhere this feature is selected, the treatment pressure is ramped up overa 5 to 20 minute period at the beginning of each treatment session,starting at a low pressure, for example 4 cmH₂O, and ramps up to thedesired full therapeutic pressure for the therapy session.

Mask Leak Control

In an embodiment of the invention, described with reference to FIGS. 2and 3, the response of the blower to changes indicative of excessive airleakage at the patient interface is controlled for improved patientcomfort and compliance and reduced possibility of disturbance.

FIG. 2 is a schematic graph of mask pressure against flow generatorpressure illustrating mask leak where the mask is not sitting properlyand sealing completely on the patient's face, for example where the maskand headgear has not been optimally adjusted or where the patient mayhave partially dislodged the mask during sleep.

With reference to FIG. 2, the blower set pressure is on the x axis andthe mask pressure on they axis.

It can be seen that the pressure lost due to the mask leak is thevertical distance between the mask pressure curve and the 45° line. In atypical situation, the mask leak at lower blower pressures will beapproximately linear with blower pressure, but above a certain blowerpressure will begin to depart more significantly from the blowerpressure as the increased pressure and flow causes a significantincrease in mask leakage. The point at which this departure commences,and the gradient of this departure, will depend on the type and fit ofthe mask to the patient, and may also vary from one session to the next,or within a therapy session, depending on the patient's sleepingposition.

In prior art APAP machines, air leakage at the mask is detected by adrop in the pressure at the nasal interface, and the response of theblower as governed by the controller is to increase the blower pressureto compensate for the leak and thus maintain adequate treatmentpressures to normalize the patient's AHI. However, in some instancesthis increased pressure merely serves to further reduce the sealing ofthe mask onto the patient's face, and the increased pressure is whollyor largely lost by increased leakage. In such instances, the volume ofair being leaked is increased with little or no net benefit to efficacyof the therapy, and with increased chance of arousal of or disturbanceto the patient and/or the bed partner.

In the present embodiment of the invention, the response of the blowerto detection of mask leak is modified.

FIG. 3 is a flowchart illustrating the steps of the mask leak controlmethod according to an embodiment of the invention.

At first detection of excessive mask leak (step 301), for example asdetermined by low mask pressure, by an excessive differential betweenthe blower pressure and the pressure at the mask or by a computed maskimpedance parameter below a certain threshold, the blower controllercauses an increase in the blower pressure (step 302) to compensate forthe leak and maintain the therapeutic pressure to desired levels, thusmoving further to the right along the mask pressure curve of FIG. 2.

Another determination of mask pressure is made (step 303) and, if theincreased blower pressure has corrected the mask pressure to compensatefor the leakage then the higher blower pressure is continued (step 304).The patient continues to be monitored for arousal (step 305).

If however the increased blower pressure has resulted in less than apredetermined pressure increase in the mask, or a greater thanpredetermined flow volume increase, this means that the blower isoperating at a low-gradient part of the mask pressure curve of FIG. 2.In this case, the controller is programmed to then recognize that thepressure increase has wholly, or mostly, been ineffectual due toincreased leakage at the mask.

When detecting this condition, the controller is programmed to thenreduce the blower pressure (step 306) (for example, by a set percentageof the treatment pressure or to the ramp start pressure) or to inhibitfurther increases in the flow generator output pressure.

The mask leak threshold against which the increased mask leak iscompared (step 308) may be a fixed quantity or proportion, for examplewhere a 2 cmH₂O increase in blower results in less than a 1 cmH₂Opressure increase at the mask.

Alternatively, the mask leak threshold may vary as a function of apatient sleep phase indicator so that a greater amount of mask leakageis tolerated if the patient is in a heavier phase of sleep and thus lesslikely to be disturbed, or if other indicators of disturbance of thepatient—such as respiratory rate—remain low. Indicators of sleep phaseare known per se in sleep medicine and include monitoring of brain wavesand/or respiration.

In a further alternative form of this embodiment, the mask leakthreshold may vary as a function of indications of flow limitation, suchas flow flattening, snore, apnea and hypopnea, or the Apnea HypopneaIndex (AHI), so that a greater amount of mask leakage is tolerated ifthe patient is more in need of higher treatment pressure. The blowercontroller is preferably programmable by the clinician to adjust themask leak threshold, or turn off the mask leak control function, forpatients with historically high flow limitation measurements.

By controlling the response of the flow generator to mask leak tooperate the apparatus at a lower mask leak portion of the maskpressure/flow generator pressure curve of FIG. 2, the amount of flowgenerator energy wasted in producing undesirable outcomes of unwantedmask leak and noise is minimized.

By reducing or capping the blower set pressure in circumstances of highmask leakage, rather than increasing the pressure further as was done inthe prior art, disturbance of the patient and/or bed partner by thenoise or air flow caused by excessive air leakage is minimized. Whilethe therapy may continue at sub-optimal pressure, it may continue toprovide some airway support and is considered that this may in manyinstances be preferable to waking the patient or having the patientremove the mask during sleep. The former is a substantial patientcomfort and compliance issue and the latter may deny the patient theentire benefit of the therapy. It is expected that, by reducing patientarousals, total sleep time and adherence to the treatment can beimproved.

Furthermore, by reducing the blower set pressure in response toexcessive mask leak, the mask may settle back into improved conformitywith the patient's face and the mask leakage be reduced, thus alteringthe mask pressure curve shown in FIG. 2 to one closer to the 45° line.

The controller may be programmed to make one or more further attempts toramp up blower pressure after a predetermined time periods, for example15 minutes, have elapsed to reassess the quality of the mask-to-patientseal.

The controller may also be programmed to monitor in real time thepatient's AHI and other patient arousal and flow limitation indicators,to detect any reduction in effectiveness of therapy at the lowerpressure. If the indicators show increased flow limitation and/orpatient arousal at the lower treatment pressure, indicative ofinsufficient treatment pressure for airway stability, the controllerwill re-increase the blower pressure (step 307).

Patient arousal may also be sensed by monitoring body position.Continual movement, if detected in conjunction with high leak, mayindicate patient arousal due to mask leak.

Snoring is indicative of airway narrowing, and may be used as anindicator that the treatment pressure is too low and must be increasedregardless of leak.

In essence, this embodiment seeks to apply the lowest pressure requiredto treat the patient effectively and limits maximum pressure incircumstances of mask leak, whereas previous treatments did only theformer. In this way, a balance is achieved between patient arousal dueto mask leak and effectiveness of the treatment, to help maintainpatient compliance with the therapy.

The controller keeps a record of incidents where the blower pressure isreduced in response to excessive mask leak, for subsequent review by theclinician to help with mask selection and adjustment for the patient.

Also, at the end of a session where excessive mask leak has beendetected, the controller may cause to be displayed on the machine amessage alerting the patient to the need to adjust the fit of the mask,and/or to contact the clinician.

The CPAP machine may have one or more leak control modes. If the CPAPmachine comprises a plurality of modes a control system may controlselecting between these modes depending for example on patientpreference and compliance levels. In a first of these modes, which forexample may be selected for less compliant patients, the machine ondetection of a leak reduces the treatment flow/pressure and maintainsthe pressure at a level below full-therapeutic to allow the mask to sealagainst the patient's face.

In the second mode of the leak control method, the flow/pressure isreduced to a sub-therapeutic pressure for a brief predetermined period,for example 15-60 seconds, to allow the mask to reseal against thepatient's face, and then is ramped back up to therapeutic pressure. Forexample, upon detection of mask leak in excess of the mask leakthreshold, the pressure may be reduced to the ramp start pressure usedfor the commencement of the therapy session, and then ramped back up tofull therapeutic pressure over a shortened ramp time, such as 50% of theramp time used at the commencement of therapy.

In a further mode, upon detection of mask leak in excess of the maskleak threshold, the pressure may be reduced by a set increment, e.g., by1 cmH₂O, and the mask leak parameter is measured again for a set periodof time. If the leak remains above the threshold, the pressure isfurther incrementally reduced, the mask leak measured again, and so onuntil the leak has been corrected or fallen below the mask leakthreshold.

After a predetermined period of operation below the mask leak threshold,the controller re-increases the flow generator pressure to re-assess themask-to-patient seal, as previously discussed.

In a further embodiment, a mask seal testing and mask fitting regimen isprovided wherein the mask is fitted to the patient in a clinical settingand the device switched to a “mask fitting” operational mode. In thismode, the flow generator is controlled to apply a normal range treatmentpressure, with the flow rate limited to a flow approximately equal to orslightly above the vent flow rate for the mask.

If the mask seals well, the pressure at the mask will be at or near fulltherapeutic pressure. If there is a substantial mask leak, this may bedetected by insufficient pressure in the mask, without the noisyoperation and large volume air leaks which the prior art lowpressure-high volume mask fitting modes regimens. In this way, the maskfit may be adjusted without undue noise and a large volume of air flowrushing past the patient's face, and a further hurdle to patientadoption of and compliance with the therapy is reduced.

In this specification, the word “comprising” is to be understood in its“open” sense, that is, in the sense of “including”, and thus not limitedto its “closed” sense, that is the sense of “consisting only of”. Acorresponding meaning is to be attributed to the corresponding words“comprise, comprised and comprises where they appear.

While the invention has been described in connection with what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the invention. Also, the various embodiments described abovemay be implemented in conjunction with other embodiments, e.g., aspectsof one embodiment may be combined with aspects of another embodiment torealize yet other embodiments. In addition, while the invention hasparticular application to patients who suffer from OSA, it is to beappreciated that patients who suffer from other illnesses (e.g.,congestive heart failure, diabetes, morbid obesity, stroke, barriatricsurgery, etc.) can derive benefit from the above teachings. Moreover,the above teachings have applicability with patients and non-patientsalike in non-medical applications.

What is claimed is:
 1. An apparatus configured for sealed delivery of aflow of breathable gas at a continuously positive pressure with respectto ambient air pressure to an entrance of a patient's airways includingat least an entrance of a patient's nares while the patient is sleepingto treat sleep disordered breathing (SDB), the apparatus comprising: ablower configured to generate the flow of pressurized breathable gas;and a controller configured to (1) adjust the blower to increase thepressure of the breathable gas when a treatment pressure is below apredetermined threshold and (2) reduce the pressure of the breathablegas or inhibit a further increase in the pressure of the breathable gaswhen the adjustment of the blower results in a less than a predeterminedincrease in the treatment pressure.
 2. An apparatus according to claim1, wherein the controller is configured to adjust the blower based on acomparison between a leak parameter and a leak threshold.
 3. Anapparatus according to claim 2, wherein the leak parameter is a leakimpedance parameter.
 4. An apparatus according to claim 2, wherein theleak threshold is based on a patient arousal index.
 5. An apparatusaccording to claim 4, wherein the patient arousal index includes atleast one of an Apnea Hypopnea Index (AHI) and a sleep phase index ofthe patient.
 6. An apparatus according to claim 5, wherein the sleepphase index is based on at least one of the patient's brain waves andrespiration.
 7. An apparatus according to claim 5, wherein the patientarousal index is based on body position.
 8. An apparatus according toclaim 5, wherein the patient arousal index is based on snoring.
 9. Anapparatus according to claim 2, wherein the leak threshold varies as afunction of indications of a flow limitation.
 10. An apparatus accordingto claim 9, wherein the indications of a flow limitation include flowflattening, snore, apnea, hypopnea, and/or Apnea Hypopnea Index (AHI).11. An apparatus according to claim 2, wherein the controller isconfigured to adjust the leak threshold or turn off a leak controlfunction.
 12. An apparatus according to claim 2, wherein the controlleris configured to maintain a record of incidents where the blower isadjusted to reduce the pressure of the breathable gas in response to anexcessive leak for subsequent review by a clinician to facilitatepatient interface selection and/or adjustment for the patient.
 13. Anapparatus according to claim 2, further comprising a display configuredto display a message at the end of a session where an excessive leak hasbeen detected that alerts the patient to adjust the fit of a patientinterface and/or contact a clinician.
 14. An apparatus according toclaim 2, wherein the controller is configured to operate in one or moreleak control modes.
 15. An apparatus according to claim 14, wherein theone or more leak control modes are selectable depending on patientpreference and/or compliance levels.
 16. An apparatus according to claim14, wherein the one or more leak control modes includes a first mode inwhich the controller adjusts the blower to reduce the pressure of thebreathable gas upon detection of a leak and maintain the pressure of thebreathable gas at a level below a full-therapeutic pressure to allow apatient interface to seal against the patient's face.
 17. An apparatusaccording to claim 14, wherein the one or more leak control modesincludes a second mode in which the controller adjusts the blower toreduce the pressure of the breathable gas to a sub-therapeutic pressurefor a brief predetermined period to allow a patient interface to resealagainst the patient's face, and then ramp back up to a full-therapeuticpressure.
 18. An apparatus according to claim 17, wherein the briefpredetermined period is 15-60 seconds.
 19. An apparatus according toclaim 14, wherein the one or more leak control modes includes a thirdmode in which the controller adjusts the blower to reduce the pressureof the breathable gas upon detection of a leak in excess of the leakthreshold to a ramp start pressure used for commencement of the therapysession, and then ramp back up to full therapeutic pressure over ashortened ramp time.
 20. An apparatus according to claim 19, wherein theshortened ramp time is 50% of the ramp time used at the commencement oftherapy.
 21. An apparatus according to claim 14, wherein the one or moreleak control modes includes a fourth mode in which the controlleradjusts the blower to reduce the pressure of the breathable gas by a setincrement upon detection of a leak in excess of the leak threshold,measure the leak parameter for a set period of time, and furtherincrementally reduce the pressure of the breathable gas if the leakremains above the leak threshold.
 22. An apparatus according to claim21, wherein the set increment is 1 cmH₂O.
 23. An apparatus according toclaim 2, wherein the controller is configured to adjust the blower tore-increase the pressure of the breathable gas to re-assess a patientinterface-to-patient seal after a predetermined period of operationbelow the leak threshold.
 24. An apparatus according to claim 1, whereinthe apparatus further comprises: a patient interface configured tosealingly engage the patient's face; and an air delivery tube fluidlyconnected to the blower and configured to deliver the pressurizedbreathable gas to the patient interface.
 25. An apparatus according toclaim 24, wherein the controller is configured to operate in a patientinterface fitting operational mode in which the controller controls theblower to apply a normal range treatment pressure in order to perform apatient interface seal testing and patient interface fitting regimen andfit the patient interface to the patient in a clinical setting.
 26. Anapparatus according to claim 25, wherein the controller is configured toadjust the blower to limit a flow rate of the breathable gas to a flowapproximately equal to or slightly above a vent flow rate for thepatient interface.
 27. An apparatus according to claim 24, wherein thecontroller is configured to adjust the blower to maintain a therapypressure at the patient interface in a range of about 2 cmH2O to about40 cmH2O above ambient air pressure.
 28. An apparatus according to claim1, further comprising a flow sensor positioned downstream of the blower,the flow sensor being configured to detect a flow rate of thepressurized breathable gas provided by the blower.
 29. An apparatusaccording to claim 24, further comprising a pressure sensor configuredto detect a pressure of the breathable gas at the patient interface. 30.An apparatus according to claim 24, wherein the less than apredetermined increase in the treatment pressure is indicative of agreater than desired gas leak or increase in gas leak at the patientinterface.
 31. An apparatus configured for sealed delivery of a flow ofbreathable gas at a continuously positive pressure with respect toambient air pressure to an entrance of a patient's airways including atleast an entrance of a patient's nares while the patient is sleeping totreat sleep disordered breathing (SDB), the apparatus comprising: ablower configured to generate the flow of pressurized breathable gas;and a controller configured to (1) compare a leak parameter to a leakthreshold to determine an excessive leak, (2) adjust the blower toreduce the pressure of the breathable gas when the controller determinesthat there is an excessive leak, and (3) continue comparing said leakparameter to said leak threshold at said reduced flow generatorpressure.
 32. An apparatus according to claim 31, wherein the leakparameter is a leak impedance parameter.
 33. An apparatus according toclaim 31, wherein the controller is configured to adjust the blower toreduce the pressure of the breathable gas to a ramp start pressure whenthe controller determines that there is an excessive leak.
 34. Anapparatus according to claim 33, wherein the controller is configured toadjust the blower to ramp up the pressure of the breathable gas to atreatment pressure over a predetermined ramp time while continuing tocompare the leak parameter to the leak threshold.
 35. An apparatusaccording to claim 34, wherein the controller is configured to adjustthe blower to halt the pressure ramping upon further determination of anexcessive leak.
 36. An apparatus according to claim 31, wherein thecontroller is configured to adjust the blower to reduce the pressure ofthe breathable gas by a pressure increment to a first reduced pressure.37. An apparatus according to claim 36, wherein the controller isconfigured to adjust the blower to incrementally further reducing thepressure in response to a detection of excessive leakage at the firstreduced pressure.
 38. An apparatus according to claim 31, wherein theapparatus further comprises: a patient interface configured to sealinglyengage the patient's face; and an air delivery tube fluidly connected tothe blower and configured to deliver the pressurized breathable gas tothe patient interface.
 39. An apparatus configured for sealed deliveryof a flow of breathable gas at a continuously positive pressure withrespect to ambient air pressure to an entrance of a patient's airwaysincluding at least an entrance of a patient's nares while the patient issleeping to treat sleep disordered breathing (SDB), the apparatuscomprising: a patient interface configured to engage the patient's face;a blower configured to generate the flow of pressurized breathable gas;an air delivery tube fluidly connecting the blower to the patientinterface; and a controller configured to (1) adjust the blower togenerate a treatment pressure, (2) adjust the blower to limit gas flowapplied to the patient to a predetermined flow rate and (3) determinethat a seal of the patient interface is insufficient based on thetreatment pressure at the patient interface being below a predeterminedvalue.
 40. An apparatus according to claim 39, wherein the controller isconfigured to determine the flow rate based on a vent flow rate of thepatient interface.